What does 2.9 figure on the clock spring means?

Those are index marks. They mean that if you wind it to the right stop then turn it back 2.9 turns it will be centered for install. For most of them the installation process is about the same. Disconnect the battery. Wat 10 minutes, remove the driver's air bag. Mark the steering wheel position on the steering shaft. Make sure the wheel is centered with the front tires straight. Remove the steering wheel and disconnect the clock spring from the wheel. Then remove the clock spring from the column. Line up the replacement and connect it and reverse the rest of the process to install the new one. Because that vehicle wasn't sold in the US (we got the Accent instead) service info isn't easy to find, but the above is about the universal process for them.

You mean I have to fully turn the steering wheel to the right? Then, turn 2.9 to the left to get the central position?

Or, after turning 2.9 to left, do I need to turn right for 2.9/2 i.e. 1.4 turn to get the central position?

Many YouTube videos are telling to turn half the 2.9 to get to the center position. It's very confusing now.

You mean I have to fully turn the steering wheel to the right? Then, turn 2.9 to the left to get the central position? - Yes, the steering system should turn about 6 turns from full left to full right. Half of that would be the 2.9 number.

On the vehicle you just make sure the front tires are straight ahead, that should be center.
Then on the part itself you rotate the inner part to the right until it stops, then turn it to the left 2.9 turns and now the part should be set up on center to install.

One thing. The above observation is valid only when the 2 arrow marks are aligned with each other.
Please see there are 2 arrow marks. What if the inner part is at random position and does not match with the arrow marks?

The inner part has marks on it that should line up as well.

You mean to say I have to first line up the 2 arrow marks, and then do the full right turn. After that, turn 2.9 to the left to center the clock spring?

Turn it to the right to the stop, then 2.9 to the left. The arrows should line up. They give you both in case it moves during install or shipping. Usually if you buy a new part it will come with it centered and a clip or pin installed to keep it there as you install it. But they also give you the turns number in case it wasn't locked or if you removed it from a vehicle and didn't know if it was still centered. The reason for that is that inside it's just a coil of flat wire in a spiral. In one direction the wire will wind onto itself and in the other it unwinds. Too much travel in either direction will damage it. Say it was installed with the arrows aligned but one turn to the right. As soon as you turned farther to the right using the steering wheel it would tear the wiring apart inside the unit. If it was too far to the left it can fold the wires over and then they break off from the flexing. So, you get all the numbers to line it up.
This is a similar situation but not your make and model but it's the same process.
https://www.youtube.com/watch?v=JlHYbPPfnkc